1. Field of the Invention
The present invention relates to a mechanism for detecting the remaining amount of films for use in an apparatus for photographing or recording by extracting sheet films one by one with suction cups from a supply magazine.
2. Related Background Art
In sheet film photographing apparatus or recording apparatus for image recording on a film with a laser beam or the like, in which film sheet are loaded in a supply magazine and are extracted one by one for photographing by means of a film extracting mechanism such as suction cups, it is important to know exactly know the amount of sheet films remaining in the supply magazine, and there have been proposed various detecting mechanisms for this purpose. As an example, the X-ray sheet film, used for so-called direct X-ray photographing for inspecting the interior of a human body by exposing said film to the X-ray transmitted by said human body, uses a substrate film of triacetate cellulose or polyester of a thickness of about 0.2 mm. Many photographing apparatus employ a method, instead of directly detecting the number of films in the supply magazine, of setting the number of films in a counter provided in the apparatus at the loading of films into the supply magazine and decreasing the count stepwise at each photographing operation. However, in such method, the remaining amount of films becomes unclear if the films are added to the supply magazine in the course of photographing operations or if the operator forgets to reset the counter, and there may result an inconvenience that the absence of film is known after the photographing operation is started. The operator is at least required to prepare new films or a new magazine when the remaining amount of films becomes low. For this reason there is preferred means for indicating the current remaining amount of films or for giving an alarm that the remaining amount has become equal to or less than a predetermined amount.
FIG. 5 illustrates a conventional system, disclosed in the Japanese Laid-open Patent Sho 63-82258, for directly detecting the films remaining in the supply magazine and informing a low remaining amount. Sheet films S are contained in a supply magazine 1. A suction cup 2 positioned thereabove is connected to a rotatable arm 3, and is further connected, through a flexible pipe 5, to a suction pump 4 generating a negative pressure. On said pipe 5 there is provided a pressure gauge 6 for measuring the negative pressure, and the signal of said suction gauge 6 is supplied to a discrimination circuit 7 for generating an alarm signal. At the rotating shaft of the arm 3 there is provided a potentiometer 8 for converting the rotating angle of the arm 3 into a resistance, and the signal from said potentiometer 8 is supplied to the discrimination circuit 7. The sucked film is fed to a photographing unit by a conveyor mechanism 9 with rollers.
The negative pressure generated by the suction pump 4 is supplied through the pipe 5 to the suction cup 2, which in this state is vertically moved by an unrepresented mechanism to film sheet S contained in the supply magazine 1, and the amount of vertical movement of the suction cup 2 is converted, through the arm 3, into the rotation of the potentiometer 8. When the suction cup 2 sucks the film sheet S, the interior of the pipe 5 changes from the atmospheric pressure to the negative pressure, and the amount of said change measured by the pressure gauge 6 is transmitted to the discrimination circuit 7. At said change from the atmospheric pressure to the negative pressure, the discrimination circuit 7 converts the amount of descent of the arm 3, namely the output of the potentiometer 8, into the remaining amount of films. Thus, if the correlation between the output of the potentiometer 8 and the remaining amount of films is determined in advance, the remaining number of film sheets S can be calculated when the pressure gauge 6 shows the negative pressure, namely when the film sheet S is sucked. When said remaining number reaches a predetermined level, an alarm is generated to request the operator to prepare new films, which will be loaded anew when the film sheet in the magazine are completely used.
In the conventional structure explained above, however, the amount of descent of the suction cup 2 may vary depending on the change in the negative pressure generated by the pump 4, the material and hardness of the suction cup 2 etc., eventually leading to an error in the measurement of the remaining amount of films, as shown in FIGS. 6 and 7. FIG. 6 illustrates a case of a hard suction cup, while FIG. 7 illustrates a case of a soft suction cup. Similarly, if the negative pressure of the suction pump 4 is strong, the film sheet S is sufficiently attracted to the suction cup 2, but, if said negative pressure is weak, the interior of the pipe 5 does not reach a predetermined negative pressure unless the suction cup 2 is sufficiently adhered to the sheet film S. In this manner the amount of descent of the suction cup 2 is dependent on the flexibility of the suction cup 2 and the negative pressure generated by the pump 4, and results in inaccurate measurement of the remaining amount of the films when said amount of descent is converted into the remaining amount of films.